This specification relates to digital information retrieval, and particularly to processing search results relating to books.
The Internet enables access to a wide variety of content items, e.g., text, video and/or audio files, web pages for particular subjects, or news articles. A search engine can identify content items in response to a user query that includes one or more search terms or phrases, and provides links to the identified content items in the form of search results.
Some search engines rank search results based on a relevance of the content item to the search query and a relative importance of the content item with respect to other content items. For example, a search engine can determine a relevance score that represents the relevance of the content item to the search query. Additionally, web pages can be ranked based, in part, on the number of web pages that include a hypertext link to each of the respective web pages. Some search engines calculate scores for content items that indicate the relative importance of a content item with respect to other content items independent of the content item's relevance to a particular search query. In some situations, however, only web pages that are identified in response to a search query are ranked. The relevance scores and ranks of web pages can be used to rank the search results.
Book content items include the text, images and other information that are presented as a book. The text on each page of a book can be scanned by a content item publisher so that the entire text of the book is available for presentation on a user device. Similar to web pages, book content items can be searched by a search engine to respond to a search query to generate a relevance score for the book content item relative to the search query. However, unlike web pages, there are not typically many hypertext links to book content items from other content items. Therefore, an optimal ordering of search results for book content items may not be achieved.